ABSTRACT
Isocyanates have become important only since the 1950s, when polyurethane resins became commercial products. The two isocyanates which form the basis of the industry are tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). MDI can be made from the diamine, formed by the reaction of aniline and formaldehyde, by the same route as TDI. TDI can be produced directly from dinitrotoluene by liquid-phase carbonylation with o-dichlorobenzene. MDI and 80–20 TDI are used for the production of polyurethane coatings. Polyurethane elastomers, produced by the reaction of TDI or MDI with short-chain polyols, can be used in the manufacture of polyurethane fibres. Sensitized workers must keep away from all contact with TDI and MDI. MDI is stable if kept in closed containers at a temperature below 5°C, but its average shelf life is only two months. In the presence of moisture, toxic compounds such as hydrogen cyanide may be formed.
